1. Field of the Invention
This invention relates to an improvement in an internal combustion engine in order to decrease engine noise, and more particularly to a bearing beam structure, used in the engine, for rigidly connecting a plurality of main bearing cap sections for rotatably supporting a crankshaft, in association with cylinder block bearing bulkheads.
2. Description of the Prior Art
In connection with engine noise, noise emitted from a cylinder block skirt section and an oil pan is mainly caused by the vibration of the cylinder block itself. In order to reduce such vibration noise, it seems enough to suppress the vibration due to explosion torque applied to a crankshaft by increasing the rigidity of the cylinder block. However, this unavoidably leads to an increase in cylinder block wall thickness and accordingly to a great increase in engine weight, thereby giving rise to new problems such as reduced fuel economy. In view of this, a variety of propositions have been made to improve the rigidity of the cylinder block while suppressing an increase in cylinder block weight. Of these propositions, particular attention has been paid to the employment of a bearing beam structure which rigidly connects a plurality of main bearing cap sections for rotatably supporting the crankshaft, in order to improve the mechanical strength of bearing cap sections and engine parts associated therewith.